The present invention relates to at least partially heat shrinkable members for forming a connection between tubular sections.
Such members may be used for connecting a variety of tubular sections together. For example, they may be used as coupling sleeves for joining plastic tubes or pipes.
A further example of the use of such members is in the formation of casings for preinsulated pipe joints.
Preinsulated pipelines for carrying fluids at non-ambient temperatures typically consist of a service or carrier pipe, covered with insulating material such as foam. The insulating material is generally encased within a jacket which may for example be made from a polymeric material, such as high density polyethylene, or a metal such as steel or aluminum. The pre-insulated pipes are connected in the field by welding the service pipe which extends beyond the insulation at each end, and then insulating and encasing the joint.
A suitable casing on the joint is a critical component of the pipeline, as it must provide a water-tight connection to the rest of the pipe and mechanical protection to the insulation. It is often desirable to employ the joint casing to facilitate the formation of foam insulation in the joint, in which case the casing serves as a mould into which the foam components are introduced usually through a foam hole in the casing side wall. In order that the casing continues to protect the joint from water ingress, it is necessary that the casing itself is not damaged, or dislocated from the joint area, or undergo distortion so that a path is created for water ingress to occur.
It has been proposed to provide heat shrinkable casing members. With some known structures of which the applicant is aware the extent of mechanical protection offered to the joint is not as great as may be considered desirable and with others the casings are not readily conformable and as easy to shrink down onto the pipe jacketing as may be desired. Further with some known structures there have been difficulties in welding on a plug to close the foam hole in the side of the casing. Further, the procedures for manufacturing these casing members have been excessively laborious and expensive. A further difficulty with known structures is that when the end portions of the casing are heated, for the purpose of shrinking them down and uniting them with the pipe jacketing, there is a tendency for portions of the casing adjacent the cavity to shrink inwardly into the cavity, thereby deforming the casing inwardly. As a result, the foam subsequently formed within the deformed casing has insufficient thickness in the inwardly deformed areas, and can present problems of insufficient protection or of excessive heat transfer through the insufficiently insulated areas. It has been proposed in U.S. Pat. No. 4,514,241 issued Apr. 30, 1985 (Maukola) to employ a coil shaped support member to preserve the desired contour of the casing during the shrinking process, but this is inconvenient and expensive because of the additional costs and inventory requirements of the coil system.
In one aspect, the present invention provides a casing member for forming a connection between tubular sections, the member having heat shrinkable end portions, for connecting on respective adjacent end surfaces of the tubular sections adjacent the joint, and a middle portion for spanning between the end surfaces of the tubular sections, the end portions formed integrally with at least a portion of the middle portion and comprising a zone having a relatively small wall thickness and the middle portion having a relatively large wall thickness.
With this arrangement, the thick middle portion, which maintains the form of a self-supporting layer at the temperature at which the end portions commence heat shrinking, and does not melt or flow at that temperature, provides excellent mechanical protection while the relatively thin heat shrinkable end portions facilitate installation since they readily conform and shrink down onto the end surfaces of the adjacent tubular sections. The said zones of the end portions tend to shrink preferentially and the relatively thick middle portion, even in the case in which it is heat shrinkable, is less readily heated to a point at which it shrinks and deforms into the cavity.
In the structure of the invention, the middle portion may be but is not necessarily heat shrinkable and can be of a wall thickness that provides a preferred degree of mechanical strength or that imparts some other desired property to the joint, while the thin zones of the end portions may be substantially thinner.
The end portions of the casing member of the invention may be of substantially uniform thickness throughout or they may have a wall portion that decreases laterally outwardly from the middle portion toward the outer ends or sides of the member. The profile may decrease in thickness smoothly or in a stepped fashion.
The wall thickness of the thinner zones (or of the thickest portions of the thinner zones in the case in which the thickness varies in the direction between the middle portion and the outer ends or sides of the member) is preferably no more than 95% the thickness of the middle portion, more preferably no more than 90%, still more preferably no more than 80%, and still more preferably no more than 70%, the thickness of the middle portion.
Desirably, the middle portion is of substantially uniform wall thickness throughout. In the event the middle portion is of varying wall thickness, reference to the thickness of the thinner zones relative to the thickness of the middle portion refer to the thickness of the thinnest portion of the middle portion.
The casing member of the invention may be formed by various techniques, for example by blow molding or rotational molding of suitable plastics materials, crosslinking, expansion and cooling to impart a heat shrink property, these methods being in themselves well known and well understood by one of ordinary skill in the art.
In a highly preferred form, however, the casing member is formed as a composite member.
In a second aspect, the invention provides a method of forming a composite sleeve member having heat shrinkable end portions comprising disposing an inner covering member on a mandrel, disposing around the inner member and mandrel a sleeve formed from a sheet that is heat shrinkable in the circumferential direction, edge portions of the sheet being bonded at an overlap portion, said sleeve extending beyond either end of the inner member, shrinking the sleeve to conform to the inner member and mandrel, bonding the shrunk sleeve to the inner member to form a composite sleeve member, and removing the composite sleeve member from the mandrel.
The inner covering member may be, for example, a tubular member, such as an extruded tube or may be a sheet wrapped around the mandrel.
This method allows the production of casing members having relatively thin heat shrinkable end portions with consistent quality and at low capital and manufacturing costs.
It further has the advantage that it allows the nature and properties of the inner member to be tailored having regard to or independently of the nature and properties of the outer heat shrink sleeve in order to provide the composite sleeve with properties or capabilities that adapt it for particular end uses.
For example, the inner member may or may not be heat shrinkable. The inner material may, for example, be formed from fibre reinforced polymer in order to obtain a higher flexural modulus. This allows the thickness of the member to be reduced without comprising the mechanical integrity of the casing member, and reduces the weight of the product.
The inner member may be a sleeve of sheet metal, such as galvanized aluminium, galvanized sheet steel or the like, in order to provide a light weight structure having mechanical rigidity. The inner member may be constructed from a combination of various materials, for example plastics and metals combined, for example in a multilayer structure.
Further, the inner member may be formed from transparent material, such as transparent polymers, and the outer sleeve may likewise be formed from transparent or semi-transparent polymers, to provide a transparent or semi-transparent casing through which it is possible to visually detect defects such as air voids that may be present in a foam formed within the casing. When such defects are detected, a repair may be carried out by drilling a hole and filling it with more foam.
In a particularly advantageous form, the inner member comprises a plastics material that is uncrosslinked, or is crosslinked to a lesser extent than the material of the sleeve, in order to facilitate heat fusing of a foam hole plug to the casing in service.
In a further modification, the casing member may be formed as a composite sleeve member made by laminating first and second layers together, at least one of these layers being heat shrinkable, forming the laminate into a sleeve, and bonding overlapped edges of the laminate together.
In a third aspect, the present invention provides a method of forming a composite sleeve member having heat shrinkable end portions comprising providing a first layer that is heat shrinkable in a heat shrink direction, laminating a second layer to the first layer, the second layer having sides disposed inwardly from the margins of the first layer, and bonding, at an overlap portion, edge portions of the laminate that are spaced apart in the heat shrink direction.
Similarly to the method described earlier, this method provides the advantage that it allows the properties of the first and second layers to be tailored to provide particular properties or capabilities for the resultant composite sleeve member. For example, the second layer, which will usually form the inner or core layer of the composite sleeve, but may in some cases form the outer layer in the sleeve structure, may for example comprise a fibre reinforced plastics material or may be uncrosslinked or crosslinked to a lesser extent than the first layer.
In the latter case, it may be preferred that the relatively uncrosslinked second layer be formed as the outer layer of the composite sleeve, in order to facilitate welding of a plastics material plug to a foam hole formed through the sleeve member in service as an insulated joint casing.
In a further aspect, the present invention provides a casing member for forming a connection between tubular sections comprising a tubular sleeve of which at least end zones are heat shrinkable, said sleeve comprising first and second plastics material layers bonded together, wherein the second layer is relatively uncrosslinked as compared with the first layer, and said sleeve having a hole through said first and second layers for introducing a liquid precursor of a foam composition to the interior of the sleeve.
As noted above, this casing member provides particular advantages of ease of welding on a plug for sealing a foam fill hole on the casing member in service.
In the preferred form, the heat shrinkable elements employed in the casing members and methods of the invention comprise cross-linked plastic materials, for example organic polymers or elastomers or mixtures thereof. Examples of suitable plastics material usable for the heat shrinkable members, and for the uncrosslinked or relatively uncrosslinked members, as well as for non-heat shrinkable or dimensionally heat stable components, are well known to those skilled in the art and need not be discussed in detail herein. Further, the methods of cross-linking the plastics materials, and the degrees of cross-linking required to provide sufficient resistance to melting to allow the cross-linked polymers to be readily heated with torch flames or the like for a period sufficient to induce shrinking are well known to those skilled in the art and need not be described in detail. Likewise, the techniques that are employed for heating and expanding or stretching or cooling suitable materials in order to impart to them a heat shrink property are conventional and well known to those of skill in the art and again need not be described in detail.
For further details of suitable plastics material compositions and of crosslinking and of stretching and expansion techniques for imparting a heat shrink property, reference may be made to U.S. Pat. No. 3,297,819 (Wetmore); U.S. Pat. No. 4,200,676 (Caponigro) and U.S. Pat. No. 4,472,468 (Tailor et al).